Question

Not sure if I can do this or not, but I’m trying to see if a type inherits from another type with a generic constraint.

Here is the class I want to find:

public class WorkoutCommentStreamMap : ClassMapping<WorkoutCommentStream>...

And here is the test

var inheritableType = typeof(NHibernate.Mapping.ByCode.Conformist.ClassMapping<>);
var isMappedObject = inheritableType.IsAssignableFrom(typeof(WorkoutCommentStreamMap));

If I change the first line to below, it works. But that defeats the purpose of my example. My fallback work around is to put a custom, non-generic, interface on all the objects I want to find and use the same call.

var inheritableType = typeof(NHibernate.Mapping.ByCode.Conformist.ClassMapping<WorkoutCommentStream>);

Answer 1

There is not an inheritance relationship between a generic type definition and a closed generic type. Therefore, IsAssignableFrom will not work.

However, I use this little extension method to achieve what your after:

public static bool IsGenericTypeOf(this Type t, Type genericDefinition)
{
    Type[] parameters = null;
    return IsGenericTypeOf(t, genericDefinition, out parameters);
}

public static bool IsGenericTypeOf(this Type t, Type genericDefinition, out Type[] genericParameters)
{
    genericParameters = new Type[] { };
    if (!genericDefinition.IsGenericType)
    {
        return false;
    }

    var isMatch = t.IsGenericType && t.GetGenericTypeDefinition() == genericDefinition.GetGenericTypeDefinition();
    if (!isMatch && t.BaseType != null)
    {
        isMatch = IsGenericTypeOf(t.BaseType, genericDefinition, out genericParameters);
    }
    if (!isMatch && genericDefinition.IsInterface && t.GetInterfaces().Any())
    {
        foreach (var i in t.GetInterfaces())
        {
            if (i.IsGenericTypeOf(genericDefinition, out genericParameters))
            {
                isMatch = true;
                break;
            }
        }
    }

    if (isMatch && !genericParameters.Any())
    {
        genericParameters = t.GetGenericArguments();
    }
    return isMatch;
}

With sample usage:

Nullable<int> value = 9;
Assert.IsTrue(value.GetType().IsGenericTypeOf(typeof(Nullable<>)));